fig8: Dose-dependent inhibition of palmitate-induced β-cell death by palmitoleate and methyl-palmitoleate. BRIN-BD11 cells were incubated with increasing concentrations of palmitoleate (squares) or methyl-palmitoleate (circles) in the presence of 0·25 mM palmitate for 18 h. The extent of cell death was estimated after staining with trypan blue. Significant inhibition (P<0·05) of palmitate-induced cytotoxicity was achieved with concentrations of 0·025 mM or greater for both palmitoleate and methyl-palmitoleate.

Mentions:
Next, methyl-palmitoleate, an analogue of palmitoleate that cannot be esterified to Co-enzyme A, was employed. As expected, exposure of cells to methyl-palmitoleate alone, failed to influence their TAG content (Fig. 7a). More significantly, the co-presence of this fatty acid failed to alter the TAG content of palmitate-treated cells, suggesting that it did not alter the metabolic routing of palmitate into TAG (Fig. 7a). To confirm this result, additional studies were conducted in which the fatty acid composition of BRIN-BD11 cell TAG was analysed after incubation of cells with palmitate and methyl-palmitoleate. As predicted, the increased incorporation of palmitate into TAG seen under these conditions was not attenuated by the presence of methyl-palmitoleate (control cells: 1·77±0·04 μg palmitate in TAG/106 cells; 0·25 mM palmitate alone: 2·57±0·28 μg (P<0·01); 0·25 mM methyl-palmitoleate alone: 1·02±0·14 μg; palmitate plus methyl-palmitoleate: 2·39±0·11 μg (not significantly different from palmitate alone)). Despite this, methyl-palmitoleate abolished the cytotoxicity induced by palmitate as revealed by cell viability assays (Fig. 7b). Indeed, its protective actions were equipotent with palmitoleate (Fig. 8) and, like palmitoleate, it also promoted β-cell growth following co-incubation with palmitate (not presented). Thus, the cytoprotective and growth-promoting properties of methyl-palmitoleate and palmitoleate were equivalent even though these fatty acids exerted differential effects on the TAG content of palmitate-treated cells.

fig8: Dose-dependent inhibition of palmitate-induced β-cell death by palmitoleate and methyl-palmitoleate. BRIN-BD11 cells were incubated with increasing concentrations of palmitoleate (squares) or methyl-palmitoleate (circles) in the presence of 0·25 mM palmitate for 18 h. The extent of cell death was estimated after staining with trypan blue. Significant inhibition (P<0·05) of palmitate-induced cytotoxicity was achieved with concentrations of 0·025 mM or greater for both palmitoleate and methyl-palmitoleate.

Mentions:
Next, methyl-palmitoleate, an analogue of palmitoleate that cannot be esterified to Co-enzyme A, was employed. As expected, exposure of cells to methyl-palmitoleate alone, failed to influence their TAG content (Fig. 7a). More significantly, the co-presence of this fatty acid failed to alter the TAG content of palmitate-treated cells, suggesting that it did not alter the metabolic routing of palmitate into TAG (Fig. 7a). To confirm this result, additional studies were conducted in which the fatty acid composition of BRIN-BD11 cell TAG was analysed after incubation of cells with palmitate and methyl-palmitoleate. As predicted, the increased incorporation of palmitate into TAG seen under these conditions was not attenuated by the presence of methyl-palmitoleate (control cells: 1·77±0·04 μg palmitate in TAG/106 cells; 0·25 mM palmitate alone: 2·57±0·28 μg (P<0·01); 0·25 mM methyl-palmitoleate alone: 1·02±0·14 μg; palmitate plus methyl-palmitoleate: 2·39±0·11 μg (not significantly different from palmitate alone)). Despite this, methyl-palmitoleate abolished the cytotoxicity induced by palmitate as revealed by cell viability assays (Fig. 7b). Indeed, its protective actions were equipotent with palmitoleate (Fig. 8) and, like palmitoleate, it also promoted β-cell growth following co-incubation with palmitate (not presented). Thus, the cytoprotective and growth-promoting properties of methyl-palmitoleate and palmitoleate were equivalent even though these fatty acids exerted differential effects on the TAG content of palmitate-treated cells.

Bottom Line:
It has been proposed that alterations in neutral lipid synthesis (particularly triacylglycerol (TAG) formation) might mediate the differential responses to saturated and unsaturated fatty acids and we have examined this proposition.By contrast, methyl-palmitoleate failed to influence TAG levels (0.25 mM methyl-palmitoleate alone: 0.95 +/- 0.06 nmol TAG/10(6) cells; methyl-palmitoleate plus palmitate: 1.5 +/- 0.05) or its fatty acid composition in beta-cells exposed to palmitate.The results suggest that monounsaturated fatty acids can promote cell viability and mitogenesis by a mechanism that does not require their metabolism and is independent of alterations in TAG formation.